1. Field of the Invention
The present invention relates to an image signal processing apparatus, an image capturing apparatus, and an image signal processing method, and more particularly to an image signal processing technique that performs peaking that emphasizes an edge portion or the like of an image displayed for easy focus adjustment.
2. Description of the Related Art
In a video camera used for a broadcasting station and a camera-built-in type video tape recorder of related art, to easily perform focus adjustment, a captured image whose high frequency components are emphasized and whose contour is clarified is displayed on a viewfinder. At this point, the captured image displayed on the viewfinder is composed by adding an image signal obtained by an image capturing apparatus such as a video camera and a peaking signal.
The peaking signal is a signal generated by extracting high frequency components from a luminance signal that composes an image signal and amplifying the extracted high frequency components. By adding the peaking signal generated in such a manner to the image signal and outputting the resultant signal to the viewfinder, the captured image is displayed on the viewfinder such that the contour portion or the like of the image is emphasized. When the photographer (also called the user) watches such an image on the screen, he or she can easily perform focus adjustment.
FIG. 1 is a block diagram showing an example of a structure of an image capturing apparatus 200 of related art, the image capturing apparatus 200 displaying a captured image whose high frequency components are emphasized. The image capturing apparatus 200 shown in FIG. 1 includes a camera section 150 and a viewfinder section 160. First, the structure of the camera section 150 will be described. The camera section 150 includes as an optical system an image-capturing lens 101, a lens barrel 102, and a prism 103. Image sensors 104B, 104G, and 104R capture an image. The image capturing apparatus 200 is structured such that image signals captured by the image sensors 104B, 104G, and 104R are processed by a video amplifier 105, an analog-to-digital conversion section 106 (hereinafter referred to as the A/D conversion section 106), a digital signal processing section 107, and a digital-to-analog conversion section (hereinafter referred to as the D/A conversion section 108).
The image-capturing lens 101 focuses an optical image of an object on respective photosensitive planes (not shown) of the image sensors 104B, 104G, and 104R and has a focus adjustment function. The lens barrel 102 is a barrel that holds the image-capturing lens 101. The prism 103 separates light entered through the image-capturing lens 101 into rays of light of three primary colors R (red), G (green), and B (blue).
The image sensors 104B, 104G, and 104R photoelectrically convert light of rays of individual colors separated by the prism 103 into image signals AB, AG, and AR and output the obtained image signals AB, AG, and AR to the video amplifier 105. The video amplifier 105 amplifies the image signals AB, AG, and AR that are output from the image sensors 104B, 104G, and 104R and outputs amplified image signals AB′, AG′, and AR′ to the A/D conversion section 106. The A/D conversion section 106 converts the image signals AB′, AG′, and AR′ that are output from the video amplifier 105 into digital image signals DB, DG, and DR, respectively.
The digital signal processing section 107 performs a digital signal process including a matrix process for the image signals DR, DG, and DB, generates a luminance signal DY and color difference signals DU and DV, and outputs the generated individual signals to the D/A conversion section 108. The D/A conversion section 108 converts the digital luminance signal DY that is output from the digital signal processing section 107 into an analog luminance signal AY and the digital color difference signals DU and DV that are output from the digital signal processing section 107 into analog color difference signals AU and AY and then outputs the generated luminance signal AY and color difference signals DU and DV to the viewfinder section 160.
The viewfinder section 160 includes a video amplifier 109, a band limit filter 110, an A/D conversion section 111, a peaking signal generation section 112, a multiplying device 113, an adding device 114, a scaling processing section 115, a matrix processing section 116, a display device drive section 117, and a display device 118.
The video amplifier 109 amplifies the luminance signal AY and the color difference signals AU and AV that are output from the D/A conversion section 108 of the camera section 150 and supplies amplified luminance signals AY′ and color difference signals AU′ and AV′ to the band limit filter 110. The band limit filter 110 is composed of a low-pass filter or a band-pass filter, limits frequency bands of the luminance signal AY′ and color difference signals AU′ and AV′ and outputs band-limited luminance signal AY″ and color difference signals AU″ and AV″ to the A/D conversion section 111.
The A/D conversion section 111 converts the luminance signal AY″ and the color difference signals AU″ and AV″ that are output from the band limit filter 110 into a digital luminance signal DY and digital color difference signals DU and DV, and outputs the luminance signal DY to the peaking signal generation section 112 and the adding device 114 and the color difference signals DU and DV to the scaling processing section 115.
The peaking signal generation section 112 extracts high frequency components from the luminance signal that is output from the A/D conversion section 111 and generates a peaking signal based on the high frequency components. Thereafter, the peaking signal generation section 112 outputs the generated peaking signal to the multiplying device 113. The multiplying device 113 multiplies a peaking level setting signal supplied from a control section (not shown) by a peaking signal that is output from the peaking signal generation section 112 and outputs a resultant peaking signal PEAK to the adding device 114.
The peaking level setting signal is a signal that sets the peaking level (intensity). The peaking level can be set by the user (photographer) through an operation section or the like (not shown). Thus, the peaking signal PEAK that is generated by multiplying the peaking setting signal and the peaking signal and that is output from the multiplying device 113 becomes a peaking signal whose level has been adjusted to a predetermined value.
The adding device 114 adds the luminance signal DY that is output from the A/D conversion section 111 and the peaking signal PEAK that is output from the multiplying device 113 and outputs a resultant luminance signal DYpk to the scaling processing section 115. The scaling processing section 115 performs pixel conversion that converts the number of pixels based on the number of pixels of the display device 118 and interlace-to-progressive (i/p) conversion to the luminance signal DYpk that is output from the adding device 114 and the color difference signals DU and DV that are output from the A/D conversion section 111. The scaling processing section 115 outputs resultant luminance signal DYpk′ and color difference signals DU′ and DV′ to the matrix processing section 116.
The matrix processing section 116 converts the luminance signal DYpk′ and the color difference signals DU′ and DV′ into RGB image signals, generates resultant image signals DRpk, DGpk, and DBpk, and outputs the individually generated image signals to the display device drive section 117. The display device drive section 117 generates a drive signal that drives the display device 118 and supplies the drive signal to the display device 118. The display device 118 is composed of a liquid crystal display (LCD) or the like and displays an image based on the drive signal supplied from the display device drive section 117.
The image signals DRpk, DGpk, and DBpk that compose an image displayed on the display device 118 are image signals to which the peaking signal generated in the peaking signal generation section 112 has been added. Thus, an image whose contour portion or the like is emphasized is displayed on the display device 118.
For example, Japanese Unexamined Patent Application Publication No. HEI 09-139952, referred to as Patent Document 1, describes a technique that emphasizes a contour portion of a captured image displayed on a viewfinder that uses a color liquid crystal display device.